Heat sensitive device



July 5, 1938 B. D. MARSHALL ET AL 2,122,320

HEAT SENSITIVE DEvicE Filed June 12, 1935 INVENTORS.

ATTORNEYS.

Patented July 5, 1938 UNITED STATES HEAT SENSITIVE DEVICE Bruce D. Marshall and Thomas J. McCormick, Detroit, Mich.

Application June 12, 1935, Serial No. 26,212

Claims. (Cl. 200-142) This invention relates to electric heating devices and more particularly to a heat sensitive fuse therefor.

An important object of this invention is to provide a fuse or circuit breaker which is sensitive to external heat and which when the critical" disintegratic particles are small and light, and

upon installation of a new fuse, the remains of the old need only be blown away.

Another object of this invention is to provide an improved construction for supporting a fuse which readily permits the insertion of new fuses. In the embodiment illustrated, the fuse is rod- Y shaped in formation and bridges two supports, each of which are provided with fastening devices to releasably secure the ends of the fuse. 'Ifhe fuse supports are adaptable to any type of heating devices, and in the embodiment illustrated herein it will be noted that the fuse is supported in readily accessible position.

Various other objects and meritorious features of the invention will more fully appear from the following specification, appended claims, and accompanying drawing, wherein;

Figure 1 is a side view partly in cross section showing the internal structure of the iron,

Figure 2 is a top view of the rear section of the iron with the cover removed,

Figure 3 is a. fragmentary plan view of the heating element and the terminals leading thereto, and

Figure 4 is a detail view showing the manner of supporting and securing the fuse.

The 'heat sensitive fuse conducts the electric current and when the critical temperature is attained immediately disintegrates into a non-conductive powdery form. This fuse is composed essentially of magnesium alloyed with one or more metals which will be described in more detail hereinafter. Magnesium forms the major metal in the alloy and constitutes substantially 90% or more of the fuse composition. It is preferred that the fuse'of magnesium alloy disintegrate at temperatures exceeding 1000 F., but it is to be understood that the relative proportions of. the ingredients can be varied tov regulate the point at which the fuse disintegrates.

In the preferred form of the invention, magnesium is alloyed with either one or more of the following metals; aluminum, manganese, cadmium and copper. In these alloys, magnesium constitutes from 91.8% to 98.5% of the whole composition. The other metals enter into combinationwith magnesium in varying proportions. Each of the metals mentioned above may form the balance of the composition, that is, form 1.5% to 8.2% of the whole fuse composition. One such alloy may consist of magnesium and manganese in which magnesium forms 91.8% to 98.5%.while manganese provides the balance of the fuse.

Another form in which the fuse of magnesium, alloy may be made is magnesium alloyed with alluminum and manganese. In this form magnesium likewise forms or more of the whole composition while the balance is made up of.

aluminum and manganese,

A still further composition may consist of all the metals listed above. Magnesium would constitute substantially 90% or more while. the balance would be made up of relatively small proportions of all these metals.

When a magnesium alloy of that composition forms a part of an electric circuit in thermal relation to a device which will heat to relatively high temperature, the alloy will instantly disintegrate into a light powdery form the moment the critical temperature is reached. In this manner, it forms an excellent fuse for such electrical heating appliances as irons and the like. The disintegrated particles are so lightthat any deposit that they form may be blown away while the fuse supporting structure is made ready for another fuse. There is no mess nor any disintegrated metal parts which are likely to clog the operating parts of, surrounding mechanism. After disintegration, the powdery material is nonconductive and it cannot short the circuit.

The fuse is supported in novel position providing ready access for replacement of a new fuse. In the drawing, reference numeral I 0 indicates the body of an electric heating iron. The iron is provided with an electric heating element 'or coil I 2 according to the usual design. The weighted portion I4 is cut away adjacent its rear end at is to form an enclosure for the electric terminals and the fuse support. The iron illustrated herein is of the type known generally as a cordless electric iron, but the invention is adaptable to any type of iron. Terminals l8 and I9 protrudlng from the rear of the iron are adapted to contact live terminals on an iron stand and connect a source of electrical power with the heating element l2. The terminals are insulated from the iron by sheets of insulative material '20, such as mica.

One of the exposed ends 22 of the heating coil is connected directly to the inner end of the terminals 18 as shown in Fig. 2. The other exposed end 24 of the heating coil is connected to. a supporting bracket 25 forming one of a pair of such brackets for supporting a fuse. This bracket is L-shaped with the base of the L secured to an extension 28 of the weighted member ll and insulatedtherefrom sheets of mica 3|]. A second fuse supporting bracket 32 is secured directly to the inner end of the terminal l9. Each of these brackets is bent over and provided with a flat top as shown in Figure 4. An adjustable clamping element 34 is secured to the top of each of these brackets. Each of these clamping devices is provided with short turned down edge portions 36 and a long depending edge portion 38. The short depending portion rests upon the top of the bracket while the longer depending edge overhangs the top of the bracket as clearly shown in Figure 4. A slot 40 is provided in one of the longer turned over edge portions 38. Bridging these brackets is rod 42 of fusible material, such as the magnesium alloy previously described. The ends of this rod are secured under the clamping elements 34. One end is inserted through the slot 4|]. Tightening of the screws H will securely grip the fuse in position. When a fuse has been disintegrated by the heat, another may be inserted by simply releasing the gripping action of the elements 34 and inserting a new rod thereunder. It is to be noted that the brackets support the rod in a readily accessible position.

The ends 22 and 24 of the coil are not connected through the intermediary of bus bars of different metalto the terminal as is the usual practice. Instead, they are connected directly to the terminals themselves. Not only is this a less expensive procedure but it prevents an unfavorable chemical action between dissimilar metals particularly when they are exposed to high temperatures and an electric circuit is delivered therethrough. This action affects the metal conductors and increases their resistance.

Various modifications will be apparent to those skilled in the art and for that reason I intend to limit myself only within the scope of the ap pended claims.

We claim:

1. A circuit breaker sensitive to external heat comprising a rod of magnesium alloy including substantially 90% or more magnesium and relatively small percentages of aluminum and manganese.

2. A heat sensitive electric fuse comprising a magnesium alloy including magnesium as the major ingredient and relatively small proportions of aluminum, manganese, cadmium and copper.

3. A heat sensitive electric circuit breaker adapted to disintegrate into a non-conductive powdery form at temperatures exceeding 1000" F. comprising an alloy of magnesium and man ganese.

4. A fuse construction comprising a pair of conductive vertical supports each having a flat topped portion, each of said supports provided with a metal element removably engageable with the top portion thereof, said elements having a relative short turned down edge adapted to rest on said top portions and a relatively long turned down edge adapted to overhang the edge of said flat portions, one ofsaid overhanging portions I reached to disintegrate into a light powdery nonconductive substance, said fuse composed of an alloy of magnesium of which magnesium comprises the major ingredient and the remainder of the composition comprises one or more of the following metals: aluminum, manganese, cadmium and copper.

THOMAS J. McCORMICK. BRUCE D. MARSHALL 

